1. Field of the Invention
This invention relates to electromagnetic motors and more particularly to linear motors employing a permanent magnet and electrical coils to produce a linear movement in either of two opposite directions.
2. Description of the Prior Art
One form of a linear motor is disclosed by Cartwright in U.S. Pat. No. 3,755,699. To produce movement, an electrical coil mounted on an armature which is supported by a non-magnetic shaft is energized to establish a polarity on end cheeks of the armature. The armature then moves between magnetic poles established by permanent magnets. Two diaphragms mounted on each end of the motor housing provide support for the armature and the non-magnetic shaft and also provide a restoring force to return the armature to a center position between oppositely polarized pole pieces when no current is flowing in the coil.
Another linear motor arrangement, employed for controlling a valve, is disclosed by Benson in U.S. Pat. No. 3,772,540. It includes a linearly movable shaft having an armature mounted thereon. A magnetic member is mounted around the periphery of the movable armature and a circular permanent magnet is mounted around the periphery of the magnetic member. Two coils are mounted in the housing with one coil on each side of the permanent magnet. The coils are employed to switch the armature back and forth between its two operating positions. The armature is switched from a first position to a second position by energizing one coil for generating a flux to nullify the permanent magnet flux holding the armature in the first position and by energizing the opposite coil for generating a flux which adds to the permanent flux flowing in the direction of the second position. The armature is then latched into the second position by the permanent magnet flux and the electrical coils are de-energized. A sleeve spring arrangement mounted on the shaft is designed with sufficient resiliency to assure valve closure and has sufficient stiffness to resist bounce-back of the valve or shaft.
These prior art structures have encountered a problem of generating a useful magnetic field of sufficient magnitude to produce an adequate force output while retaining a compact motor structure. Cartwright's separate magnet and pole piece arrangement contributes to flux leakage; thus, the useful magnetic field, and thereby the efficiency of the motor, is decreased. Benson's use of a magnetic conducting material between the circular permanent magnet and the armature increases flux leakage and his disclosed circular permanent magnet structure precludes use of samarium cobalt.
These prior art structures also have encountered problems with detecting a defective coil and with complete motor failure once a coil becomes defective. Cartwright employs only a single electrical coil; thus, coil failure renders his device inoperative. Benson employs two coils connected in series; thus, a coil failure also renders his device inoperative.
The present invention solves these problems by providing a compact motor structure designed to obtain maximum efficiency, by providing a segmented samarium cobalt permanent magnet structure mounted directly adjacent a moving armature, by providing a redundant electrical coil arrangement with each coil independently controlled, and by providing a monitoring circuit for detecting and isolating a defective coil and for providing an alarm upon occurrence of such a defect. The object of this invention is to solve the aforementioned and other problems encountered by the prior art and thus, develop a highly efficient compact linear motor with high performance capability.
One of the objects of this invention is to provide an electromagnetic motor structure with a higher magnetic field concentration than previous structures of comparable size and a structural arrangement to provide maximum utilization of this higher magnetic field.
Another object is to provide an electromagnetic motor with an output movement continuously controlled in proportion to an input electrical signal.
Another object is to provide an electromagnetic motor with a means to prevent latching of the motor.
A further object is to provide an electromagnetic motor with an electrical coil control arrangement capable of detecting and isolating a defective coil and providing an alarm upon occurrence of such defect and capable of continuing motor operation despite a coil failure.